Modbus TCP communication between CPU317-2PN & MOXA gateway

Hi,

We have a query on S7 300 Modbus TCP/IP communication.

 System Overview

•     CPU 317 PN/DP (inbuilt PN port used) is configured as Modbus TCP/IP client and the MOXA gateways – 2 nos. connected as modbus TCP server through SCALANCE switch.

•     Each MOXA gateway has 4 serial RS 485 interfaces & 1 ethernet interface (modbus TCP/IP). Each serial interface connected to a serial loop to the Power monitoring units. On each serial loop max 25 slave devices are connected. Similarly are total 8 serial loops connected to both gateways.

•     There are 2 connections (gateway - 01 & 02) configured in Modbus DB PARAM. 

•     In user program the logic is made to poll the slave devices one by one under connection-01 & 02

•     The system architecture enclosed for reference

 Present Scenario

•     Using CONTROL DAT DB we are moving the connection ID, unit ID, DB No, Start address & Length

•     Under Connection-01 the modbus loop devices are communicating fine.

•     While switching over to connection-02 (i.e. Connection ID = 2), the data transfer not happening and the status showing that connection establishment remians "True" and there is no error.

 Please clarify to resolve this.

Thanks,

Dina

Hi,

how many calls of the MODBUSPN block do you have? If you have only one call then the behaviour of the blocks is correct.

The ID is a init parameter of the block. When you change this parameter you need to reinitialize the block. Normaly this is done by stopping and restarting the CPU so the block can be called in the OB100.

You have two options:

Either you can have to calls of the MODBUSPN block, one for each connection. 

Or you can connect to one gateway-> read all the data you need -> disconnect from that gateway -> change the IP in the Modbus Parameter DB -> connect to the second gateway.

 Dear Gwawl,

Thanks for your reply.

One call of MODBUSPN block used in user program. For initialization it also called in OB100. 

Under "MODBUS_PARAM" DB the 2 connections were configured. I have changed the ID of "CONTROL_DAT" to change connection but it is not working.

I have tried with one connection in "MODBUS_PARAM" and changed the IP for gateway 2. It didn't worked and after doing PLC restart it is working for 2nd connection. The same problem while am switching to connection 1 also.

Can you please send any sample program for Modbus TCP client with multiple TCP servers (Both Inbuilt PN & CP343-1) 

Thanks,

Dina

Gwawl

Hi,

how many calls of the MODBUSPN block do you have? If you have only one call then the behaviour of the blocks is correct.

The ID is a init parameter of the block. When you change this parameter you need to reinitialize the block. Normaly this is done by stopping and restarting the CPU so the block can be called in the OB100.

You have two options:

Either you can have to calls of the MODBUSPN block, one for each connection. 

Or you can connect to one gateway-> read all the data you need -> disconnect from that gateway -> change the IP in the Modbus Parameter DB -> connect to the second gateway.

New question published by e_skazem is split to a separate thread with the subject Convert Modbus TCP to Modbus RTU, FB108want a reg_key.

Best regards
Min_Moderator